4′-[[4-methyl-6-(1-methyl-1H-benzimidazol-2-yl)-2-propyl-1H-benzimidazol-1-yl]methyl]biphenyl-2-carboxylic acid (Telmisartan) has the formula as given below

Telmisartan and the physiologically acceptable salts are useful as angiotensin antagonists, particularly an angiotensin-II-antagonist, may be used to treat hypertension, cardiac insufficiency, to treat ischaemic peripheral circulatory disorders, myocardial ischaemia (angina), to prevent the progression of cardiac insufficiency after myocardial infarct, to treat diabetic neuropathy, glaucoma, gastrointestinal diseases and bladder diseases.
U.S. Pat. No. 5,591,762 discloses Telmisartan, methods for its preparation and methods of pharmaceutical formulations using Telmisartan. The process disclosed in U.S. Pat. No. 5,591,762 involves (Scheme-1)                i. Reacting 4-methyl-6(1-methylbenzimidazol-2-yl)-2-n-propyl-1H-benzimidazole with t-Butyl 4′-(bromomethyl)-2-biphenyl-2-carboxylate in the presence of an acid binding agent in a solvent or mixture of solvents.        ii. It further discloses the formation of a mixture of the 1 and 3 isomers and their separation by chromatography using a substrate such as silica gel or aluminum oxide to obtain t-Butyl-4′-[4-Methyl-6-(1-methyl-1H-benzimidazol-2-yl)-2-n-propyl-1H-benzimidazol-1-yl-methyl]biphenyl-2-carboxylate.        iii. Hydrolysis of the t-Butyl 4′-[4-Methyl-6-(1-methyl-1H-benzimidazol-2-yl)-2-n-propyl-1H-benzimidazol-1-yl-methyl]biphenyl-2-carboxylate with trifluoro acetic acid in dimethyl formamide followed by purification with silica gel column and crystallization.        

U.S. Pat. No. 6,358,986 discloses the form A, form B and mixtures of the polymorphs of Telmisartan. This patent also discloses that polymorphic form A, melts at 269±2° C., characteristic band at 815 cm−1 in the IR spectrum is considered as prior art form. The polymorphic form B melts at 183±2° C. (by DSC), characteristic band at 830 cm−1 in IR spectrum. The disclosed process for polymorphic form B and mixtures involves dissolving crude Telmisartan in a mixture of water, formic acid and organic solvents, at elevated temperature, and precipitating with a suitable base followed by drying under vacuum at 120-125° C. U.S. Pat. No. 6,358,986 further discloses that after centrifugation, the product begins to change to polymorphic form A depending on the temperature, pH, retention time and water content towards the end of the drying.
U.S. Pat. No. 6,737,432 disclosed crystalline sodium salt of Telmisartan characterized by melting point (245±5° C.), XRD, processes for preparation and use thereof for preparation of a pharmaceutical composition. It further discloses the solvates and hydrates of crystalline Telmisartan sodium. The disclosed process for preparation of Telmisartan sodium involves the reaction of sodium salts such as sodium hydroxide, sodium hydride, sodium carbonate, sodium bicarbonate or sodium alkoxides with Telmisartan in an organic aprotic solvent. The alternate process disclosed for preparation of Telmisartan sodium salt is by treatment of Telmisartan acid addition salts, hydrochloride salt with bases such as sodium hydroxide, sodium hydride, sodium carbonate, sodium bicarbonate or sodium alkoxides in a suitable solvent, may be water and/or a suitable alcohol mixed with an aprotic organic solvent by heating the mass along with charcoal to temperature to <40° C., filtering to remove the insolubles, distilling the solvent followed by azeotropic removal of solvent, left to crystallize, filteration, optionally washing with above mentioned aprotic solvent and drying.
The U.S. Pat. No. 6,737,432 further characterizes the Telmisartan hydrochloride, melting point 278° C., the disclosed process for preparation of Telmisartan hydrochloride involves the reaction of t-Butyl 4′-[4-Methyl-6-(1-methyl-1H-benzimidazol-2-yl)-2-n-propyl-1H-benzimidazol-1-yl-methyl]biphenyl-2-carboxylate with aqueous hydrochloric acid (37%) in glacial acetic acid by refluxing, partial removal of solvent by distillation, dissolution in water, charcoal treatment, crystallization by stirring for about 12 hrs at 23° C., filtration, washing with water, acetone and drying at about 60° C.
U.S. Pat. Application No. 2003/139608 disclosed and claimed the process for the preparation of pure 4-methyl-6(1-methyl benzimidazol-2-yl)-2-n-propyl-1H-benzimidazole by purifying the crude product obtained by reaction of 2-n-propyl-4-methyl-1H-benzimidazole-6-carboxylic acid on reaction with N-methyl-o-phenylenediamine preferably in the form of salt, by charcoal treatment of said crude reaction product.
The prior art processes discloses for preparation of Telmisartan involving the column chromatographic purifications of intermediate and/or final stage. The process disclosed for preparation of Telmisartan hydrochloride involves the usage, distillation of glacial acetic acid along with hydrochloric acid, which requires acid resistant equipment. Hence there is a need for a simple process for preparation of Telmisartan without involving the column chromatographic purifications and distillation of acids in various stages during the process.